The present invention relates to a semiconductor device, and is preferably usable for, for example, a semiconductor device using a nitride semiconductor, and a method for manufacturing a semiconductor device.
In recent years, attention has been paid to semiconductor devices each using a III-V group compound having a larger band gap than that of silicon (Si). Among them, development has been pursed on semiconductor devices using gallium nitride (GaN) having advantages such as 1) large breakdown electric field, 2) large saturated electron velocity, 3) large thermal conductivity, 4) being able to form a favorable hetero junction between AlGaN and GaN, and 5) being a nontoxic and high-safety material.
Further, for high breakdown voltage and high-speed switching characteristic, development has been pursued on a semiconductor device which is a power MISFET (Metal Insulator Semiconductor Field Effect Transistor) using gallium nitride, and is capable of normally-off operation.
For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2010-206110), there is disclosed a nitride semiconductor device having a gate recess structure. Then, there is disclosed a technology of surface-stabilizing the nitride semiconductor device, and thereby suppressing the current collapse.
Further, in Patent Document 2 (Japanese Unexamined Patent Publication No. 2008-205392), there is disclosed a compound semiconductor device in which the protective insulation film covering the surface of the compound semiconductor region is formed in a double layer structure of a first insulation film and a second insulation film having different properties.
Further, Patent Document 3 (Japanese Unexamined Patent Publication No. 2012-44003) and Patent Document 4 (Japanese Unexamined Patent Publication No. 2013-77629) disclose nitride semiconductor devices, and each disclose a technology of suppressing the current collapse.
Whereas, in Non-Patent Document 1, there is disclosed the relation between the stoichiometric composition of SiN and the collapse amount. In Non-Patent Document 2, there is disclosed the relation between the refractive index and the collapse amount of the protective film of a monolayer thermal CVD silicon nitride film. Furthermore, Non-Patent Document 3 discloses as follows: for the protective film of a silicon nitride film, when the refractive index is 2.01, the collapse amount is minimum. Further, in Non-Patent Document 4, there is disclosed a nitride semiconductor device using a nitrogen (N)-rich SiN film and a SiN film formed by low temperature deposition CVD as the protective films.